In a mobile communication system, if a building is built in the vicinity of a base station, or if the installation status of a base station in the vicinity of the base station changes, the radio environment related to the base station changes. Therefore, conventionally, drive tests to measure and collect the radio environment are carried out by an operator with using a measurement vehicle on which a measuring instrument is installed.
Such measurement and collection may contribute to network optimization (for example, coverage optimization due to adjustment of parameters of the base station). However, there are problems in that the number of processes and cost increase.
Thus, in 3GPP (3rd Generation Partnership Project), which is a project aiming to standardize a mobile communication system, MDT (Minimization of Drive Tests) for automation of the measurement and collection using user terminals has been specified on and after Release 10 (see Non-patent Document 1, for example).
An example of the MDT is Logged MDT. In the Logged MDT, the user terminal in an idle state stores MDT measurement logs related to radio environments measured based on an instruction from a network and then transmits (reports) the stored MDT measurement logs to the network later.